The invention relates to an enclosed separator unit for incorporation into a gas supply of a fuel cell system, for separating liquid from the gas supply. The separator unit has a housing and a separator that is enclosed in and/or in thermal contact with, a gas space in the housing. It also has a line system for draining the liquid away from the separator.
Fuel cell systems of this type are used as mobile energy sources for example in vehicles. The mode of operation of the fuel cell systems is based on the fact that electrical energy is generated by an electrochemical reaction of a fuel (for example, hydrogen) with an oxidant (for example, ambient air), or conversion from the chemical energy of the hydrogen.
To implement the electrochemical process, fuel cell systems conventionally comprise a cathode area, an anode area and a membrane arranged between these areas. The fuel is passed through the anode area and the oxidant is passed through the cathode area, the membrane being permeable to ion migration which takes place in the process. It has become apparent that, in operation, the membrane must be kept at a defined humidity, so that it does not suffer premature wear. Accordingly, water management components are provided in both the anode and cathode gas supply, to ensure that the humidity on both sides of the membrane is kept at the desired level.
A water management component which is often used is separator unit, which is incorporated into the anode gas supply, means. This separator unit has the task of separating excess water—or more generally liquid—out of the anode gas supply means.
German Patent Document DE 102 16 953, for example, discloses a supply device for a fuel cell stack in which a condenser is provided in the cathode gas supply for separating water from the exhaust air originating from the fuel cell. This document does not address the structural design and arrangement of the condenser.
One object of the present invention is to improve the operating reliability of a fuel cell system, taking particular account of the gas supply.
This and other objects and advantages are achieved by the enclosed separator unit according to the invention, which is suitable and/or constructed for incorporation into a gas supply, (preferably an anode gas supply or a cathode gas supply) of a fuel cell system. The fuel cell system is preferably mobile, and in particular is designed for use in vehicles. It comprises one or more fuel cell stacks, which have a plurality of fuel cells (preferably, more than 100 fuel cells per fuel cell stack) each of which comprises a cathode and an anode area separated by a membrane (e.g., PEM).
The fuel cell system may optionally comprise a refuelable tank or a reformer for providing the fuel, in particular hydrogen.
The separator unit, which is suitable and/or constructed for separating liquid from the gas supply, comprises a separator, preferably in the form of a condenser, which separates the liquid from a gas stream. The separator is enclosed in a housing, which likewise forms a constituent part of the separator unit, the separator being placed in a gas space located inside the housing and/or being in thermal contact with this gas space. Preferably, the gas space is sealed in a liquid-tight and/or gas-tight manner relative to the surrounding environment by the housing. The housing is preferably smaller than ten times the volume of the separator, in particular smaller than five times this volume, in particular smaller than three times this volume. Preferably, a level sensor is arranged on the separator, which sensor measures the height of the liquid collected in the separator. The level sensor is preferably likewise positioned in the housing and/or in the gas space.
To drain away the liquid, the separator unit has a line system which is constructed for example with an ejector for draining the liquid into the environment, into a storage tank for liquids or into a humidifier for humidifying the working gases, i.e. the fuel and the oxidant.
According to the invention, the enclosed separator unit may comprise at least one fluid dynamically active functional component which is arranged in the line system (in particular is connected for flow), and which is arranged in the gas space (i.e., in the housing of the separator unit).
In the invention it was identified that the operating reliability of fuel cell systems (particularly their gas supply systems), is also heavily influenced by environmental conditions. At ambient temperatures of below 0° C. in particular, components in the gas supply means tend, to freeze or ice up, which may severely impair the functionality and thus the operating reliability of the gas supply and ultimately of the entire fuel cell system.
In order to achieve in particular a frostproof gas supply design, it is now proposed according to the invention to arrange the separator together in a common housing with at least one further fluid dynamically active functional component of the line system for draining away the liquid. With this arrangement the media stream of the gas supply, which passes through, the separator is used to introduce heat into the separator unit, and thus the temperature of both the separator and the at least one fluid dynamically active functional component is adjusted by means of the media stream.
In a preferred embodiment of the invention, the further functional component takes the form of a valve and/or a filter, preferably a drain valve and/or a drain filter, which respectively controls or filters the outflow of liquid from the separator. It is precisely these two functional components, which in some configurations are located in the line system between separator and exhaust, that (due to their installation position) are subject to the risk of freezing or icing up at temperatures of below 0° C. Due to the arrangement according to the invention of these functional components in the actively or passively heated, or temperature-adjusted, installation space, this risk is markedly reduced or even ruled out
In an advantageous further embodiment of the invention, one or more heating devices are incorporated in the housing. Heating devices are preferably understood to mean active heating devices, which provide heat by converting external energy, or passive heating devices, which provide heat using heat exchangers.
In a possible alternative embodiment of the heating device according to the invention, a portion of the cooling water circuit of the fuel cell system is passed through the housing and/or a heat exchanger is incorporated into the housing which is in thermal contact with the cooling water circuit. Once the cooling liquid of the cooling water circuit displays a temperature of above 0° C. (at the latest a short time after start up of the fuel cell system), the temperature of the gas space and thus of the functional components in the gas space may be adjusted as a result of thermal coupling between housing and cooling water circuit.
In another alternative embodiment, the heating device is an electrical heating device, preferably in the form of a cartridge heater. It is particularly preferable for the cartridge heater to be arranged in the gas space directly adjacent the functional component(s).
In a further alternative embodiment, the heating device constitutes a portion of the anode gas supply (particularly the purge branch thereof), some of which portion extends through the housing of the separator unit. Alternatively, a heat exchanger may also be incorporated into the housing which is in thermal contact with the anode gas supply means, particularly the purge branch.
The stated heating devices may be used during start-up or during operation below 0° C. to thaw or keep liquid condensed—out water, particularly in the area of thawed surfaces.
In a preferred further embodiment of the invention, at least one further fluid dynamically active functional component is incorporated into the housing and/or into the gas space of the housing. In this instance, advantage is taken of the fact that not only functional components which are constituent parts of the line system for draining the liquid away from the separator but also other functional components may have their temperature adjusted by incorporation into the housing or into the gas space.
It is particularly preferred in this case that the further functional components comprise constituent parts of the anode gas supply (particularly a constituent part of a or the purge branch of the anode gas supply). Since the media stream in the anode gas supply means has to be kept at a high temperature (for example, around 80° C.), the temperature of the separator or said functional components of the line system may be adjusted by incorporating the functional components into the housing, or—if an additional heating device is provided the temperature of the functional components of the anode gas supply means may be adjusted by the additional heating device together with the separator and the functional components of the line system.
In accordance with this concept, in a preferred further embodiment of the invention, the further functional components take the form of valves and/or filters of the purge branch, thus of purge valves and/or purge filters.
In addition to the above possibilities for implementing a heating device, the heating device may be constructed and/or arranged for direct heating of the purge branch, the heating device preferably taking the form of an electrical heating device.
In a particularly preferred structural embodiment of the invention, the functional components are arranged such that, when the separator unit is installed, liquids remaining in the intake of the functional components (particularly in the intake of the drain valve and/or of the drain filter) flow back into the separator under the effect of gravity.
Alternatively or in addition, the portion of the anode gas supply, the purge branch, the purge valve and/or the purge filter, is/are arranged such that, in the idle state, residual liquid flows back into the anode gas supply, in particular into a main branch of the anode gas supply means.
In order to assist the liquids to flow back in areas at less risk of frost, the liquid-conveying surfaces of the functional elements are preferably provided with a repellent, preferably a hydrophobic coating, which assists the liquid to run off.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.